File:Uranography. and Atlas (1850) (14783124325).jpg

Identifier: uranographyatlas00kend (find matches)
Title: Uranography. & Atlas
Year: 1850 (1850s)
Authors: Kendall, Bzra O. (from old catalog)
Subjects:
Publisher: (n.p.)
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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apparent diameter of the disc of the moonis divided into 12 equal parts, called digits. Thegreatest eclipse of the moon may amount to 22digits; this is called the quantity of the eclipse. The duration of a lunar eclipse depends partlyupon its quantity, and partly upon the velocityof the moons motion across the shadow, which isthe same as her motion from the sun. This mo-tion is swiftest when the moon is in her perigee;and the duration of a central eclipse will then beshortest, though the moons diameter and that ofthe shadow, at the place where the moon passesthrough it, are greatest. The longest durationof a partial eclipse is about 2 hours 18 minutes,and that of a total eclipse 4 hours 38 minutes. In Fig. 1, on the following plate, let S be thecentre of the sun, E that of the earth, and a, band c, the centre of the moon in its orbit, a por-tion of which is represented by the arc m, n. Thespace g9 T, h, included between the tangent linesH, h, T, and G, g, T, will represent the shadow
Text Appearing After Image:
(303) T 304 ECLIPSES OF THE MOON. or umbra, and E, T, the axis of the shadow. Theentire disc of the sun will be hidden by the earthfrom all points within that space. The space be-hind the earth, included between the tangent linesH, g, n, and G, h, m, which touch the sun andearth on opposite sides, is called the penumbra;it is a frustrum of a cone, only a section of whichis represented in the figure. From any pointwithin this frustrum, but not in the shadow, apart of the suns disc only can be seen. When the moon arrives at the point m, she be-gins to lose sight of the sun, and in passing fromm to c the visible portion of the suns disc dimin-ishes to a very small segment, near the point H;the moon, as seen from the earth, grows more andmore faint until she reaches the shadow, at whichtime the eclipse begins upon the eastern side ofthe moon. The eclipse ends when the moonreaches the position a9 where the western limb ofthe moon just touches the shadow. It is impossible to determine by ob

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